This application is based on Patent Application No. 2000-366294 filed Nov. 30, 2000 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method which eject inks of different colors from at least two print heads for recording, and more particularly to a method of reducing degradation of image quality due to bleeding of ink.
2. Description of the Related Art
Printing apparatus used as printing means for printing images and others in printers, copying machines and facsimiles, and those used as print output devices for combination electronic equipment and workstations, including computers and word processors, are all designed to record images on a recording material (hereinafter referred to also as a print medium), such as paper and plastic thin plate, according to image information (all output information including character information).
Such printing apparatus may be classed into an ink jet system, a wire dot printing system, a thermal printing system and a laser beam printing system according to the printing method. Of these systems, the printing apparatus of the ink jet system (hereinafter referred to as an ink jet printing apparatus) ejects ink from a printing means including a print head onto a print medium to perform printing and has a variety of advantages, such as a capability to easily increase resolution, a high printing speed, a low noise and a low cost compared with printing apparatus of other systems.
In recent years as the importance of color outputs such as color images grows, a number of color ink jet printing apparatus with high quality matching that of a silver halide photography have been developed.
Such an ink jet printing apparatus improves the printing speed by using a print head which has a plurality of print elements integrally arrayed therein with high degree of accumulation and also a plurality of ink nozzles and liquid paths formed therein with high degree of accumulation in a one-to-one relationship with each print element. To print a color image, a plurality of such print heads are provided one for each color ink to be ejected.
FIG. 9 is a schematic diagram showing a nozzle array in an example of the print head.
In FIG. 9 reference number 101 represents a black print head with an array of 320 nozzles at a degree of accumulation of 600 nozzles per inch (600 dpi) to eject a black ink. 102, 103 and 104 represent cyan, magenta and yellow ink print heads, respectively, each with 128 nozzles with a degree of accumulation of 600 nozzles per inch (600 dpi). Y indicates a direction in which the print paper is fed (sub-scan direction).
The black print head 101 uses all 320 nozzles in a monochrome print mode for printing a monochromatic image such as sentences and, in a color mode, uses 128 nozzles from the top of the drawing to print a color image such as a photographic image. The color print heads 102, 103, 104 are used only in the color mode using all 128 nozzles. The color nozzles for the color mode are shifted 128 nozzles in the paper feed direction from the black nozzles.
Now, the color mode operation will be explained.
FIG. 10 shows the construction of main components of the printing apparatus that prints on paper by using the print heads described above. In the figure, 201 represents ink jet cartridges (printing means). These comprise four color ink tanks containing black, cyan, magenta and yellow inks and four print heads 202 corresponding to these ink tanks.
Designated 203 is a paper feed roller (sub-scanning means) which, together with an auxiliary roller 204, holds the print paper P and rotates in the direction of arrow to intermittently feed the print paper P in the Y direction. Denoted 205 are a pair of paper supply rollers which, like the rollers 203 and 204, hold the print paper P as they rotate. The rotating speed of the paper supply rollers 205 is set lower than that of the paper feed roller 203, generating a tension in the paper so that it is fed without slack.
Reference number 206 represents a carriage (main scanning means) that supports the four ink jet cartridges 201 and reciprocally moves (or scans) in the main scan direction X perpendicular to the paper feed direction Y. When the print heads 202 are not performing the printing operation or are subjected to the ejection recovery operation, the carriage 206 stands by at its home position h indicated by a dashed line.
The carriage 206 situated at its home position h, upon receiving a print start command, prints on the paper over a width of {fraction (128/600)} inches (about 5.42 mm) by using 128 nozzles of the print head 202 as it scans in the X direction. When the printing is finished up to the side end of the paper, the carriage returns to the home position h and again performs the scan in the X direction. After the first printing operation is finished and before the second printing starts, the paper feed roller 203 rotates in the direction of arrow to feed the paper a distance equal to {fraction (128/600)} inches in the Y direction. In the second and subsequent printing operations, the color print heads are also used.
At each scan of the carriage 206, the printing over a width of {fraction (128/600)} inches using the print heads 202 and the paper feeding are repeated until one whole page is printed. Such a print mode is referred to as a one-pass print mode.
The one-pass print mode is explained in detail by referring to the drawings.
FIG. 11 is a schematic diagram showing the printing method in the one-pass print mode.
In FIG. 11, reference number 301 and 302 represent a black print head and a color print head. The color print heads 302 for cyan, magenta and yellow are all arranged in line in the sub-scan direction, so the print time difference between the black print head 301 and any of the color print heads is almost equal. That is, the time difference between each of the color print heads and the black print head in the first and second scans is one scan period T for all color print heads. Hence, in FIG. 11 the color print heads are shown as one print head for simplicity.
Here, a so-called one-way printing (hereinafter refereed to also as an 1-pass printing) is employed in which the printing is done only when the carriage moves forward. Thus, one scan period means the time it takes for the carriage to make a forward movement for printing and a backward movement for returning. In a so-called two-way printing (hereinafter refereed to also as a 2-pass printing) in which the printing is done in both the forward and backward scans of the carriage, the one scan period means the time taken by the carriage to make a forward and a backward movement for printing and return to its original position. A print area A represents an area that is printed by the 128 nozzles arrayed in the Y direction. That is, the print area A is 128 nozzles wide in the Y direction.
In the first scan, the black print head 301 completes printing all print data that is to be printed in the print area A. After this, the print paper is fed in the Y direction a distance equal to the length of 128 nozzles.
Next, in the second scan, the color print head 302 completes printing all color print data that is to be printed in the print area A. When the first and second scans are finished, the printing of black and color print data in the print area A is completed.
As described above, in the 1-pass print mode, when the black print area and the color print area adjoin each other, the color printing is performed with a time difference T after the black printing has been done. Thus, the color ink may be printed adjacent to the black ink before the black ink is fixed on the paper. In that case, the black and color inks may bleed to mix together, degrading the quality of printed image.
Another print mode used in the ink jet printing apparatus is a multi-pass print mode. In this multi-pass print mode, the print data to be printed in a print area is printed in two or more overlapping passes over the same area to complete the printing.
Next, the multi-pass print mode will be explained.
Here, we take for example a so-called 2-pass printing in which the printing is done in two overlapping passes on the same print area. In the 2-pass printing, when it receives a print start command, the carriage 206 situated at the home position h moves in the X direction to print on the paper over a width of {fraction (64/600)} inches (about 2.71 mm) by using the black print head 301.
Dots that are printed during this scan are derived from the image data to be printed by thinning out it to one-half with a predetermined mask pattern. When the printing up to the side end of the paper is completed, the carriage 206 returns to the home position h and again moves forward in the X direction for printing. After the first scan is finished and before the second scan starts, the paper feed roller 203 rotates in the direction of arrow to feed the paper {fraction (64/600)} inches in the Y direction.
During the second scan, too, only the black print head 301 is used. In the third and following scans, the color print head 302 is also used. All the print areas are scanned twice by the printing head of each color and are completed by printing the printing data thinned out by the mask pattern in each scan respectively. The above description concerns a multi-pass print mode that performs two overlapping scans. A multi-pass print mode that performs M overlapping scans over the same print area is referred to as an M-pass print mode.
FIG. 12 shows 2-pass mask patterns used in the 2-pass print mode.
In the figure reference number 401 represents a mask pattern for a first pass and 402 represents a mask pattern for a second pass.
The mask patterns shown here are 4xc3x974 masks, in which image data overlapping black pixels constitutes pixel data to be printed in each pass (scan). The mask pattern for the first pass 401 and the mask pattern for the second pass 402 have checkerboard patterns and are complementary to each other. The mask patterns are not limited to those shown in FIG. 12 and may use other patterns as long as the first- and second-pass mask patterns each have a print density of 50%.
The relation between the 2-pass print mode and the 2-pass mask patterns will be explained in detail by referring the drawings.
FIG. 13 is a schematic diagram showing the printing method in the 2-pass print mode.
In FIG. 13, reference numbers 301 and 302 represent black and color print heads, respectively, as in the case of FIG. 11. In the first to the fourth scan, the time differences between the adjoining scans are all T (one scan period). A print area B represents an area whose length in the Y direction is equal to a distance covered by 64 nozzles. That is, the length in Y direction of the print area B is equal to one-half the length of nozzles used.
In the first scan, the black print head 301 prints the print area B using a first-pass mask pattern (print density 50%). Then, the print paper is fed a distance equal to 64 nozzles in the Y direction.
In the second scan, the black print head 301 prints the print area B using a second-pass mask pattern (print density 50%) to complete a black ink image. Then, the print paper is fed a distance of 64 nozzles in the Y direction.
In the third scan, the color print head 302 prints the print area B using the first-pass mask pattern (print density 50%). Then, the print paper is fed a distance of 64 nozzles in the Y direction.
In the fourth scan, the color print head 302 prints the print area B using the second-pass mask pattern (print density 50%), thus completing the printing in the print area B.
When in the 2-pass print mode the black print area and the color print area adjoin each other, the color ink that adjoins the black ink printed in the first scan with a print density of 50% is printed a time difference of 2T later with a print density of 50%. Therefore, the black ink and the color ink do not bleed and mix together as severely as in the 1-pass print mode. As for the black ink printed in the second pass with a print density of 50%, because the color ink that is printed a time difference of T later has a print density of 50%, the degree of bleeding and mixing of this color ink and the black ink is smaller than in the 1-pass print mode.
Similarly, in a multi-pass print mode with three or more passes, the degree of ink bleeding is smaller than in the 1-pass print mode. The greater the number of passes, the smaller the degree of ink bleeding and the smaller the possibility of mixing of the color ink and the black ink.
The checkerboard pattern of the 2-pass print mode described above is proposed in Japanese Patent Application Laid-open No. 55-113573.
In the multi-pass print mode, however, an increase in the number of passes results in an increase in the printing time, giving rise to a problem that a sufficient printing speed cannot be obtained. When the number of passes is reduced to increase the printing speed, the problem of bleeding and mixing of different color inks becomes more serious. Hence, realizing the printing at an increased speed and with a reduced color mixing has been one of the problems very difficult to solve in the ink jet printing apparatus.
An object of the present invention is to solve the problems described above and provide an ink jet printing apparatus and an ink jet printing method which eject inks of different colors from at least two print heads for recording and can reduce degradations in image quality caused by color mixing due to bleeding of ink and enable high-speed printing.
According to a first aspect, the present invention provides an ink jet printing apparatus which comprises: a printing means having a plurality of print heads with a plurality of nozzle groups, each of the nozzle groups having a predetermined number of print nozzles, each of the print heads ejecting one of inks of different colors; a main scanning means for moving the printing means relative to a print medium in a main scan direction; a sub-scanning means for moving the print medium a distance equal to the nozzle group relative to the printing means in a sub-scan direction, the sub-scan direction crossing the main scan direction; and a masking means for thinning out print data to a predetermined print density and supplying the thinned out print data to the associated nozzle group, the print data representing an image to be printed on each of print areas that are moved intermittently by the sub-scanning means; wherein the plurality of different nozzle groups are main-scanned M times (Mxe2x89xa72) over each of the print areas to print the print data to complete the image; wherein the print heads perform the main scans over each of the print areas at different print densities.
According to a second aspect, the present invention provides an ink jet printing apparatus which comprises: a printing means having a plurality of print heads with a plurality of nozzle groups, each of the nozzle groups having a predetermined number of print nozzles, each of the print heads ejecting one of inks of different colors; a main scanning means for moving the printing means relative to a print medium in a main scan direction; a sub-scanning means for moving the print medium a distance equal to the nozzle group relative to the printing means in a sub-scan direction, the sub-scan direction crossing the main scan direction; and a masking means for thinning out print data to a predetermined print density and supplying the thinned out print data to the associated nozzle group, the print data representing an image to be printed on each of print areas that are moved intermittently by the sub-scanning means; wherein the plurality of different nozzle groups are main-scanned M times (Mxe2x89xa72) over each of the print areas to print the print data to complete the image; wherein the print heads successively execute the main scans over each of the print areas in such a way that, of the print heads adjoining in a printing order, the print head located at a front position in the printing order performs an Mth main scan with a lower print density than that of an Nth main scan (1xe2x89xa6N less than M).
According to a third aspect, the present invention provides an ink jet printing apparatus which comprises: a printing means having a plurality of print heads with a plurality of nozzle groups, each of the nozzle groups having a predetermined number of print nozzles, each of the print heads ejecting one of inks of different colors; a main scanning means for moving the printing means relative to a print medium in a main scan direction; a sub-scanning means for moving the print medium a distance equal to the nozzle group relative to the printing means in a sub-scan direction, the sub-scan direction crossing the main scan direction; and a masking means for thinning out print data to a predetermined print density and supplying the thinned out print data to the associated nozzle group, the print data representing an image to be printed on each of print areas that are moved intermittently by the sub-scanning means; wherein the plurality of different nozzle groups are main-scanned M times (Mxe2x89xa72) over each of the print areas to print the print data to complete the image; wherein the print heads successively execute the main scans over each of the print areas in such a way that, of the print heads adjoining in a printing order, the print head located at a rear position in the printing order performs a first main scan with a lower print density than that of an nth main scan (1 less than nxe2x89xa6M).
According to a fourth aspect, the present invention provides an ink jet printing apparatus which comprises: a printing means having a plurality of print heads with a plurality of nozzle groups, each of the nozzle groups having a predetermined number of print nozzles, each of the print heads ejecting one of inks of different colors; a main scanning means for moving the printing means relative to a print medium in a main scan direction; a sub-scanning means for moving the print medium a distance equal to the nozzle group relative to the printing means in a sub-scan direction, the sub-scan direction crossing the main scan direction; and a masking means for thinning out print data to a predetermined print density and supplying the thinned out print data to the associated nozzle group, the print data representing an image to be printed on each of print areas that are moved intermittently by the sub-scanning means; wherein the plurality of different nozzle groups are main-scanned M times (Mxe2x89xa72) over each of the print areas to print the print data to complete the image; wherein the print heads successively execute the main scans over each of the print areas in such a way that, of the print heads adjoining in a printing order, the print head located at a front position in the printing order performs an Mth main scan with a lower print density than that of an Nth main scan (1xe2x89xa6N less than M) and the print head located at a rear position in the printing order performs a first main scan with a lower print density than that of an nth main scan (1 less than nxe2x89xa6M).
According to a fifth aspect, the present invention provides an ink jet printing apparatus which comprises: a printing means having a first and a second print head with a plurality of nozzle groups, each of the nozzle groups having a predetermined number of print nozzles, each of the print heads ejecting one of inks of different colors; a main scanning means for moving the printing means relative to a print medium in a main scan direction; a sub-scanning means for moving the print medium a distance equal to the nozzle group relative to the printing means in a sub-scan direction, the sub-scan direction crossing the main scan direction; and a masking means for thinning out print data to a predetermined print density and supplying the thinned out print data to the associated nozzle group, the print data representing an image to be printed on each of print areas that are moved intermittently by the sub-scanning means; wherein the plurality of different nozzle groups are main-scanned M times (Mxe2x89xa72) over each of the print areas to print the print data to complete the image; wherein the first and second print heads successively execute the main scans over each of the print areas in such a way that, of the first and second print heads, the first print head located at a front position in a printing order performs an Mth main scan with a lower print density than that of an Nth main scan (1xe2x89xa6N less than M).
According to a sixth aspect, the present invention provides an ink jet printing apparatus which comprises: a printing means having a first and a second print head with a plurality of nozzle groups, each of the nozzle groups having a predetermined number of print nozzles, each of the print heads ejecting one of inks of different colors; a main scanning means for moving the printing means relative to a print medium in a main scan direction; a sub-scanning means for moving the print medium a distance equal to the nozzle group relative to the printing means in a sub-scan direction, the sub-scan direction crossing the main scan direction; and a masking means for thinning out print data to a predetermined print density and supplying the thinned out print data to the associated nozzle group, the print data representing an image to be printed on each of print areas that are moved intermittently by the sub-scanning means; wherein the plurality of different nozzle groups are main-scanned M times (Mxe2x89xa72) over each of the print areas to print the print data to complete the image; wherein the first and second print heads successively execute the main scans over each of the print areas in such a way that, of the first and second print heads, the second print head located at a rear position in a printing order performs a first main scan with a lower print density than that of an nth main scan (1 less than nxe2x89xa6M).
According to a seventh aspect, the present invention provides an ink jet printing apparatus which comprises: a printing means having a first and a second print head with a plurality of nozzle groups, each of the nozzle groups having a predetermined number of print nozzles, each of the print heads ejecting one of inks of different colors; a main scanning means for moving the printing means relative to a print medium in a main scan direction; a sub-scanning means for moving the print medium a distance equal to the nozzle group relative to the printing means in a sub-scan direction, the sub-scan direction crossing the main scan direction; and a masking means for thinning out print data to a predetermined print density and supplying the thinned out print data to the assocaited nozzle group, the print data representing an image to be printed on each of print areas that are moved intermittently by the sub-scanning means; wherein the plurality of different nozzle groups are main-scanned M times (Mxe2x89xa72) over each of the print areas to print the print data to complete the image; wherein the first and second print heads successively execute the main scans over each of the print areas in such a way that, of the first and second print heads, the first print head located at a front position in a printing order performs an Mth main scan with a lower print density than that of an Nth main scan (1xe2x89xa6N less than M) and the second print head located at a rear position in a printing order performs a first main scan with a lower print density than that of an nth main scan (1 less than nxe2x89xa6M).
According to an eighth aspect, the present invention provides an ink jet printing method using an ink jet printing apparatus, the ink jet printing apparatus comprising: a printing means having a plurality of print heads with a plurality of nozzle groups, each of the nozzle groups having a predetermined number of print nozzles, each of the print heads ejecting one of inks of different colors; a main scanning means for moving the printing means relative to a print medium in a main scan direction; a sub-scanning means for moving the print medium a distance equal to the nozzle group relative to the printing means in a sub-scan direction, the sub-scan direction crossing the main scan direction; and a masking means for thinning out print data to a predetermined print density and supplying the thinned out print data to the assocaited nozzle group, the print data representing an image to be printed on each of print areas that are moved intermittently by the sub-scanning means; wherein the plurality of different nozzle groups are main-scanned M times (Mxe2x89xa72) over each of the print areas to print the print data to complete the image; wherein the print heads perform the main scans over each of the print areas at different print densities.
According to a ninth aspect, the present invention provides an ink jet printing method using an ink jet printing apparatus, the ink jet printing apparatus comprising: a printing means having a plurality of print heads with a plurality of nozzle groups, each of the nozzle groups having a predetermined number of print nozzles, each of the print heads ejecting one of inks of different colors; a main scanning means for moving the printing means relative to a print medium in a main scan direction; a sub-scanning means for moving the print medium a distance equal to the nozzle group relative to the printing means in a sub-scan direction, the sub-scan direction crossing the main scan direction; and a masking means for thinning out print data to a predetermined print density and supplying the thinned out print data to the associated nozzle group, the print data representing an image to be printed on each of print areas that are moved intermittently by the sub-scanning means; wherein the plurality of different nozzle groups are main-scanned M times (Mxe2x89xa72) over each of the print areas to print the print data to complete the image; wherein the print heads successively execute the main scans over each of the print areas in such a way that, of the print heads adjoining in a printing order, the print head located at a front position in the printing order performs an Mth main scan with a lower print density than that of an Nth main scan (1xe2x89xa6N less than M).
According to a tenth aspect, the present invention provides an ink jet printing method using an ink jet printing apparatus, the ink jet printing apparatus comprising: a printing means having a plurality of print heads with a plurality of nozzle groups, each of the nozzle groups having a predetermined number of print nozzles, each of the print heads ejecting one of inks of different colors; a main scanning means for moving the printing means relative to a print medium in a main scan direction; a sub-scanning means for moving the print medium a distance equal to the nozzle group relative to the printing means in a sub-scan direction, the sub-scan direction crossing the main scan direction; and a masking means for thinning out print data to a predetermined print density and supplying the thinned out print data to the associated nozzle group, the print data representing an image to be printed on each of print areas that are moved intermittently by the sub-scanning means; wherein the plurality of different nozzle groups are main-scanned M times (Mxe2x89xa72) over each of the print areas to print the print data to complete the image; wherein the print heads successively execute the main scans over each of the print areas in such a way that, of the print heads adjoining in a printing order, the print head located at a front position in the printing order performs an Mth main scan with a lower print density than that of an Nth main scan (1xe2x89xa6N less than M) and the print head located at a rear position in the printing order performs a first main scan with a lower print density than that of an nth main scan (1 less than nxe2x89xa6M).
According to an eleventh aspect, the present invention provides a printing method in an ink jet printing apparatus, the ink jet printing apparatus including: a printing means having a plurality of print heads with a plurality of nozzle groups, each of the nozzle groups having a predetermined number of print nozzles, each of the print heads ejecting one of inks of different colors; a main scanning means for moving the printing means relative to a print medium in a main scan direction; and a sub-scanning means for moving the print medium a distance equal to the nozzle group relative to the printing means in a sub-scan direction, the sub-scan direction crossing the main scan direction; wherein the ink jet printing apparatus performs printing based on print data supplied from an externally connected host device; the printing method comprising the steps of: thinning out the print data to a predetermined print density by the host device, the print data representing an image to be printed on associated one of print areas that are moved intermittently by the sub-scanning means; sending the thinned out print data from the host device to the ink jet printing apparatus; supplying the thinned out print data to the associated nozzle group; and main-scanning the plurality of different nozzle groups M times (Mxe2x89xa72) over each of the print areas to print the print data to complete the image; wherein the print heads perform the main scans over each of the print areas at different print densities.
As described above, in the ink jet printing apparatus of this invention that ejects inks of different colors from at least two print heads to print an image, a so-called multi-pass printing can be performed in such a way as to reduce color mixing due to bleeding of inks of different colors and enable high-speed printing of a high-quality image, without increasing the number of passes.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.